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First American A superbly preserved skeleton found in an underwater Mexican cave is that of a teenage girl that lived around 13,000 years ago, an analysis of her remains has revealed.

Study of the DNA extracted from the girl's wisdom tooth sheds light on a longstanding debate about the origins of the Western Hemisphere's first people and their relationship to today's Native American populations.

The findings, reported in today's journal Science, support the theory that modern Native American populations are directly related to Ice Age humans who first crossed into the Americas over a land bridge linking Siberia to Alaska between 26,000 and 18,000 years ago, rather than from separate migrations from different parts of Eurasia.

In 2007, divers exploring a cave deep beneath the jungles of Mexico's eastern Yucatán peninsula discovered the girl's nearly complete skeleton alongside bones of more than two dozen beasts including sabre-toothed tigers, cave bears, giant ground sloths and an elephant relative called a gomphothere.

The divers named her "Naia", a water nymph from Greek mythology.

One of the divers, Alberto Nava, recalled the moment Naia was spotted — her skull resting atop a small ledge.

"It was a small cranium laying upside down with a perfect set of teeth and dark eye sockets looking back at us," says Nava.

The petite, slightly built girl — about 1.47 metres tall — is thought to have been 15 or 16 years old when she died.

She may have ventured into dark passages of a cave to find freshwater and fallen to her death into a 30-metre deep bell-shaped pit dubbed Hoyo Negro, "black hole" in Spanish, says study co-author archaeologist James Chatters of Applied Paleoscience.

He says the "inescapable pit — more than 40 metres below sea level — was "a time capsule of the environment and human life" at the end of the Ice Age.

The pit was dry when she fell but Ice Age glaciers melted about 10,000 years ago, inundating the caves with water.

Radiocarbon dating and comparison of the remains of other species in the cave with her reveal she lived between 12,000 and 13,000 years ago.

Genetic heritage

Scientists have long have debated the origins of the first people of the Americas. Many scientists think these hunter-gatherers crossed the former land bridge and subsequently pushed into North and South America starting perhaps 17,000 years ago.

But the most ancient New World human remains have confused scientists because, like Naia, they have narrower skulls and other features different from today's Native Americans.

This led to speculation that these earliest New World people might represent an earlier migration from a different part of the world than the true ancestors of modern Native Americans.

But mitochondrial DNA showed she belonged to an Asian-derived genetic lineage shared only by today's Native Americans.

This indicates cranial and other differences between the earliest New World human remains and today's Native Americans are due to evolutionary changes that unfolded after the first migrants crossed onto the land bridge, say the researchers.